Motor-controlling mechanism.



J. D. IHLDBR. MOTOR GONTROLLING MECHANISM.

APPLIOATION FILED 001131, 1908.

1,064,224, Patented June 10, 1913.

{b m N @i gn-uenfoc: qvibmcaocs b I WA pa fyg UNITED STATES PATENT OFFICE.

IOHN D. IHLDER, OF NEW YORK, N. 'Y., ASSIGNOR TO OTIS ELEVATOR COMPANY, OF JERSEY CITY, NEW JERSEY, A CORPORATION OF NEW JERSEY.

MOTOR-CONTROLLIN G MECHANISM.

Specification of Letters Patent. Patented June 10 1913 Application filed October 31, 1908. Serial No. 460,524.

To all'wlwm 2'35 may concern Beit known that 1, JOHN D. IHLonR, a citizen of the- United States, residing in -New York, in the county .of New York and elevators and ammunition hoisting mecha-' nism as i used in fortifications and naval vessels.

One object of the invention is the provision of improved means for automatically controlling an electric motor to stop a car or carrier at predetermined points in its travel, regardless of the speed, load or friction. Another object of the'invention is the provision of automatic controlling mechanism for the motor, which will eflect a gradual or gentle stop of the car or carrier at intermeiate points in its travel and a rapid stop at the limits of travel.

A further object of the invention is to produce a motor and controlling mechanism therefor in which the automatic operation in stopping the motor at the limits of car travel differs from that ciiected manually, in accordance with the varying requirements and conditions for the ditterent stops.

Other objects of my invention will appear hereinafter, the novel coinbiiiatioiis of elemerits being pointed out in the claims annexed hereto.

Referring to the accompanying drawing which illustrates diagrammatically the motor controlling apparatus and electrical circuits therefor embodying my invention, S designates a switch by means of which an operator may start, stop and reverse the hoisting apparatus.

T designates a safety or emergency switch, and is pretcrably located close to the switch S so as to be within easy reach of the operator. Two of automatic stop switches 1, 2, 3, 1-. and l, 2-, 31 K, 5' may be located adjacent the upper limit of car travel. The first-named set is adapted to be engaged by a cam C carried by the car as the latter approaches its upper limit of travel, while the latter set is engaged by a similar cam lV carried by the counterbalance weight or car when the car approaches its lower limit of travel, both cams being of suilicient length to be in engagement with all of the switches of a set at one time.

The automatic stop switches 1, 2, 3, l, 5 and l, 2, 3, 4', 5 may be arranged at vary ing distances from each other to suit various conditions met"with in practice. Fur thermore, these stop switches may be replaced by other switching means arranged to be automatically operated by any moving part of the hoisting apparatus, such as the winding drum shaft. The drawing shows separate switches operated directly by the car or counterbalance weight when the latter is used, merely for simplicity and clearness.

M designates a hoisting motor which is operatively connected to the car or carrier by means of suitable hoisting mechanism, the latter not being shown since it forms no part of the present invention and may be of any suitable construction.

R and R are motor reversing switches, and, while the. same may be of any suitable construction, I prefer the type of switches herein shown, the same being substantially like those shown in U. S. Patent No. 704,336. granted to me on July 8, 1902.

B designates the magnet coil of thcmsual spring or gravity actuated electrically re leased friction brake, while B is a resistance normally in parallel therewith.

The motor illustrated herewith is ot the direct current, compound wound type, this type of motor being particularly adapted for hoisting purposes in that it combines the powerful starting torque at low speeds of the series wound motor with the substantially constant speed characteristics of the shunt wound motor. The series and shunt field windings are designated by D and F, respectively G designates an extra field winding having in series with it a sectional resistance ll, which latter is cut out of or into circuit by means of a load magnet L. A suitable rcsist-ance be used in place of-the extra field winding.

b: is an electromagnetic switch which controls a circuit to the load magnet L.

A designates an accelerating ""Hr i 1 llll gliku which efiects the short-circuiting of the motor starting resistance and series field w1nd-' Having briefly described the various parts of the apparatus embodying my invention, I will now go into a more detailed description of these parts and their coiiperation, at" the same time tracing out the various c1r cuits. V

The light lines represent the operating,

brake and shunt field circuits and the cir-' cuit of the load magnet L, while the heavy lines denote the main or motor circuits, the

extra field circuits being shown by lines of medium thickness.

The potential switch P comprises a magnet winding 33 and core 54, the latter being adapted when magnetized to hold a series of insulated contacts in electrical engagement with corresponding fixed contacts directly above. These contacts are designated by 34, 35, 36, 37 and 38. Other contacts 39 are in a similar manner normally held out of engagement with eachother. The poten tial switch P under normal conditions has its magnet winding 33 energized, thereby maintaining its contacts-closed, as shown. The circuit for-this windin 33 is as follows,from the positive mam through the contacts 35, contacts of slack cable switch 1, contacts 34, to and through the-magnet winding 33 and resistance 33, through the automatic stop switches 5 and 5, emergency switch T, fuse 4:0, and contacts 37 and 36, to the negative main. 1

In order to illustrate the operation of the system, let the handle of the operating switch S beunove'd a short distance to the right until the segment 6 engages the fixed contact 8. This operation closes a circuit to the reversing switch R from the positive main through contacts 35 of the potential switch, fuse 40, through the magnet windin 48 of the switch K, wire 53, winding 18 o? the reversing switch R, through the automatic stop switch 4, switch contacts 8, 6 and 7, emergency switch T, wire 55, fuse 40, contacts 37 and 3 6 of the potential switch P, and to the negative main. This circuit energizes the magnet switch K and reversing switch R and they will operate in a manner to be pointed out later.

' The. reversing switches R and R each comprises a magnetic core or plunger to which are fastened arms carrying contacts, such'as 12, 13, 1a and 15. In the path of these movable contacts are fixed contacts, such as 10, 11, 16 and 17 which are adapted to be engaged by the movable contacts. The

winding 18 of switch R, when energized,

tends to lift its core to which are connected the contacts 12, 13, 14k and 15, causing the contacts 12 and 13 to engage the fixed contacts 10 and 11 respectively. The movable contacts 14 and'15 will at the same time be moved away from the fixed contacts 16 and 17 respectively. The winding 19, however, tends when energized to pull its core and connected contacts in a downward direction. A rocker arm 52 is operatively connected. to

the switches R and R and prevents both switches being in their extreme upward or downward positions'at the same time. This interlocking device is shown diagrammatically on the drawing, the precise construction being shown in Patent No. 704,336,

granted to me on July 8, 1902, and entitled Reversing switch motor. As beforepointedout, the circuit estab lished by moving the operating switch S in a. right-hand direction includes the ma net windings of the switches K and R. The

switch K being thus energized, raises its core and connected contact plate, thereby open-circuiting the contacts-4C9. The winding 18 of switch It being also energized,

raises its core, and by so doing brings the contacts 12 and 13.=into electrical engagement with the fixed contacts 10 and 11', respectively. 'At the same time the rocker arm 52 allows the contacts 14 and 15 of the reversing switch R to engage the contacts 16 and 17, respectively. The closing of these reversing switch contacts establishes circuits to the motor and brake magnet B. The motor circuit may be traced from the positive main through the potential switch contacts 35, wire 55, contacts 11 and 13 of the reversing switch R, wire 57, contacts 15 and 17' of the reversing switch R, winding 19, brushQl, through the armature of the motor M, brush 20, contacts 16 and 14 of the reversing switch R, to and through the sectional starting resistance H and H, series field winding D, and by-wire 58 and potential switch contacts 37 and 36 to the negative main. A circuit is at the same time closed to the brake magnet, which may be traced from the contact 11 to the contacts 13, 12 and 10, wire 56, to and through the brake magnet coil B, wire 63, contacts 38 and 36, to the negative main; The clming of the reversing 'switch R not only closes a circuit through-the motor armature and brake magnet, but also a circuit through the Shunt field andextrafield windings, the armature circuit including the winding 19 which operates to pull itscore in a-downward direction, thereby maintaining the contacts 14;, i6 and 15, 17 in close electr cal engagement. The shunt field circuit may be traced from the positive main through the contacts 35, wire contacts 11, i3 and 12, wire 59, field winding E, wire 58, contacts 3? and 36, to the negative main. The extra field circuit is from the motor brush 2i, winding 19, contacts 17, 15, wires 57 and 59, to and through the extra field G, resistance 3, contacts 24. and 23 of magnet switch. F, contacts 14' and 16 to the motor brush 20. The extra field is therefore connected as a shunt to the motor armature.

Under the present conditions the motor armature receives current limited in amount by the starting resistance H and H, the se ries field, shunt field and extra field are energized, the current in the latter being limited in amount by the resistance J in series therewith. The brake is also released by the magnet B and the motor starts and runs at slow speed in a direction to lift the load. The next operation is to move the switch farther toward the right until the contact segmentb bridges the fixed contacts 7, 8 and 9. A circuit is thereby closed through the winding of magnet switch F, which may be traced from the positive main through contacts 35, wire 55', contacts 11 and 13, wire 57, contacts 12 and 13, to and through the winding of magnet switch F, automatic stop switch 1, contacts 9, 6 and 7 cl. switch S, emergency switch T, wire 55, fuse L0" and to the negative main 58. The magnet of switch F is now-energized to raise its core and connected contacts 23 and 26 into electrical engagement with the fixed contacts 22 and 25, respectively, at the same time carrying the contact 23 out of engagement with the contact 24%. By closing the contacts and 23, the starting resistance H is short-circiilited, allowing more current to flow to the motor armature. At the same time a circuit to the winding 82 of the accelerating magnet A is established by way of the contacts and 26. This circuit may be traced from the armature brush 21, through in iet coil 19', contacts 1-7, 15 and 13, to and through the winding 32, contacts 26 and 25 of switch F, through a portion of the starting resistance H (the resistance H being short-circuited by the contacts 22 and 23 at this time), contacts 14- and 16, to the motor armature brush 20. The winding 32 is therefore connected across or in shunt to the motor armature and a portion of the starting resistance H, and its energization depends upon the counter-electro-motive force of the rotating armature. The winding 32 of the accelerating magnet when sutliciently energized operates to close a series of contacts-27, 28, 29, 30 and 31, which contacts may be arranged in any one of several well known ways-so that they will always operate in a certain predetermined order. The movable contacts are here shown as being at varying distances from their'respective fixed contacts, and so arranged that the cont-acts 27 will close first, then the contacts 28, and so on until finally the contacts 31 will close. The contacts 27 28 and 29 operate to short-circuit sections of the starting resistance H, the contacts 30 shortcircuit a portion of the starting resistance, together with a portion of the series field D, and the lastcontacts 3.1 operate to shortcircuit the remainder of the series field.

At the same time that the switch F operates to connect the contacts 23, 22 and 26, 25, the contacts 23 and 2a are separated, and thus the circuit to the extra field winding G is broken at these contacts. The motor now accelerates to full speed, with all of the starting resistance cut out of the armature circuit, and, being excited by the shunt field alone, runs at substantially constant speed.

In order to stop the motor and thus arrest the upward movement of the car and load, the switch S is moved back to its initial or central position. The switch segment 6 first passes out of electrical engagement with the contact 9, thereby interrupting the circuit for the magnet coil of switch F and causing the separation of the contacts 22, 23 and 25, 26, the contacts 23 and 24 once more coming into engagement. The separation of the contacts 22 and 23 reinserts the resistance H in the armature circuit, while the separation of the contacts 25 and 26 interrupts the circuit to the winding 32 of the accelerating magnet A and the latter operates to reinsert the resistance H and series field D in the armature circuit. The closing of the contacts 23 and 24 connects the extra field G and resistance J in series therewith across the armature brushes, producing a dynamic brake action, and by increasing the field strength of the motor, helps to reduce its speed. The switch S is next brought to its initial central position, the segment 6 passing oil of the contact 8. Since the contact 8 is connected through the automatic stop switch 4 to one terminal of the reversing switch magnet 18, the latter is de'e'nergized, allowing its core and connected contacts to drop, thus separating the contacts 10, 12 and 11,-13, respectively, of the reversing switch R, and thereby cutting ofi the current supply to the motor and brake magnet B. The brake magnet B contains a resistance B connected in parallel with it, this parallel connection including the automatic stop switches 2 and 2 which are normally closed as shown. The function of this resistance B is to furnish a path for the brake magnet discharge which occurs when the supply circuit to the brake magnet is broken at the reversingswitch con;

cient to allow the brake mechanism to stop the motor may be varied considerably, as it depends largely upon the amount of resistance B in circuit, and also upon the construction of the brake magnet itself. For this reason the resistance B is so arranged that more or less of it may be connected in circuit, and this adjustable feature is indicated on the drawing in the usual ner. As soon as theswitch S is brought back to ,IHELII- center, the circuit to the winding 48 of mag-1. not switch K, which is connected in series with the reversing switch magnets 18, 18,

is broken and the contacts 49 are electrically connected together. closesa circuit from the armature brushes to the winding 51 of the load magnet L, including the resistance 50 in series-therewith. This circuit may be traced from the brush 20, through contacts 16, let and 14, wire 60,

- winding 51 energized by virtue of its concontacts 49 of switch'K, resistance 50, winding 51, wire 59, contacts 12, 13, 12', 13, 15', 17, winding 19, and to the brush 21. The winding 51 of the load magnet L in series with the resistance 50 is thus connected directly across the motor brushes and is therefore subjected to the varying potential of the armature. The load magnet L having its nection across the motor armature, will close more or less of its contacts to short-clrcult the resistance J in series with the extra field accordlng to the counter-electro-motive force of the armature. Since this counterelectro-motive force will depend upon the speed and load upon the car or carrier, the amount of resistance J automatically cut out of the extra fieldcircuit by the magnet L will also depend upon the speed and load on the car. -Thus it follows that the reduction in speed of the motor armature, due to the dynamic brake action produced by the extra field G, will be proportional to the speed and load" on thecar. Atabout this time the brake magnet-B has become suiii c'iently denergized to allow the brake apparatus to be gradually applied and the motor and connected car or carrier comegently to rest.

The operation just described is the normal operation when the car is started and stopped. by the manipulation of the switch S, such operation taking place at any position of the car between the upper and lower normallimits.

In order to illustrate the operation of stopping by means. of the automatic stop switches 1, 2, 3, 4,- 5, etc, we will assume This connection Loeagaze that the switch S is maintained in its ex tre'me right-hand positionwith the motor running at full speed, the shunt field alone being excited. As the car approaches at full speed the upper limit of its travel, the cam C carried by the car will first engage and open the automatic. stop switch 1. Since this switch includes-the circuit to the magnet switch F, the latter will become denergized, thereby opening its contacts and energizing the extra field G. This operation is the same in effect 'aswhen the switch segment #6, was moved away from the contact 9 by manual means, as before described; that is, the starting resistance and series field are cutinto circuit and the extra field, having in series with it the resistance J, is connected across the armature brushes. The speed of the motor is thus reduced. The next operation-is when the cam' carried by the upwardly traveling dar engages and opens the ing speed conditions, it being merely a preparatory operation. The automatic stop switch 3 is next engaged and in this case the contacts of this switch will be closed, thereby closing a circuit to the winding 51 of the load'magnet L connected across the armature brushes. This circuit may be traced from the wire 59 which is connected through the contacts of the reversing switch R to the armature brush 21 as before pointed out, through the winding 51, automatic stop switch 3, wire .50, through the contacts 14, 14', 16', to" the armature brush 20. The winding 51 is thus connected directly across *the armature brushes, the resistance 50 and contacts 49 of the switch K being left out of circuit.

When the automatic switch .3 is operated, the speedoff the motor, and its counter-electro-m'otive force'have-beenreduced and the winding-I51 of the load magnet is therefore subjecte to a reduced potential. When the load magnet 'is brought into operation by operating the switch S with the car in an intermediate position, this ;magnet will in most cases be subjected to substantially the full line potential, since the operator will usually center the? operating switch S diatc stops as produced by the operator,

since these stops should be gentle. It is desirable, however, to have the dynamic retardation' at amaximum when the stopis 'action of the automatic stop switches preparatory to stopping, the load conditions on the motor are altered. This change of load may be caused by additional friction or by reason of the counterbalance weight having bottomethor by other causes which tend to vary the load on the motor. In some cases, such as double cage ammunition hoists, the

final stop position of the upper carrier may be varied to correspond to the different ele vations of the gun. If, under the above conditions, the dynamic brake remains active to the full extent for which it'has been adjusted to operate while the car was running under normal conditions of load,

any variation in load at this time would tend to place an additionalduty on the motor which it could not ropcrly perform with the full dynamic bra ing power, and conse-' quently the final stop position would not be correct. It is with special reference to the above conditions that the load magnet L is arranged to open more or less of its contacts and thus reinsert in the extra field circuit the sectional resistance J or a portion thereof, depending upon the reduction in potential of the motor armature as the latter slows down, thereby increasing the power of the motor again in proportion to the existing load conditions so that when the friction brake is finally applied to stop the motor the car Rvill automatically come to, rest exactly at the required landing. In this manner the load magnet L automatically controls the sectional resistance J for. all variations of speed and load, either cu'ttin out or rein sorting the proper amount 0? resistance in series with the extra field. winding and always short-circuiting or open-circuiting the difi'erent. resistance sections in predetermined order or sequence as before described. I,

While the'load magnet'L may be con: structed substantially like the accelerating magnet A, that is, a single winding operating any desired number of contacts to cut out or short-circuit a sectional resistance, there is this distinction: The magnet A is arranged as before described to close a series of contacts in a predetermined order or sequence of operation; the magnet L is so arranged that it not only closes its contacts in a predetermined order, but alsov causes them to open again in a predetermined order as well. This operation may be brou ht about in any. one of several ways. As ustrated on the diagram, a series of movable contacts,

such as 41, 42, 43, form the armatures for the stationary contacts or pole pieces d1, 42, 43 of the load magnet L. Graduated springs" 44:, -15 and 46 surrounding the stems carried by the movable contacts hold the latter normally up against a stationary supporting piece 47. When the magnet coil 51 is excited, the weakest spring 44 permits the contact 41 to be ulled down into engagement with the contact il first, thereby short-circuitin a section of the resistance J. The contadt 4:2. is next pulled down to short-circuit another section of the resistance, and finally the contact 43 will be operated against the upward pressure of-the strongest spring at, and thereby short-circuit another section of the resistance, leaving only a small portion of the resistance J in the circuit. It will be understood that the current through the magnet coil 51 may at times be strong enough to operate only a portion of the movable contacts, and also that the number of; contacts and sections of resistance controlled thereby may be varied to obtain any desired degree of refinement in operation. Should the strength of load ma net L be reduced, part or all of the mova e contacts will be operated to. open position in the inverse order of their initial operation, the strength of the springs determining the order in which they will overcome the weakenedpull ot the magnet and lift their con? tacts. The amount of' resistance J short-circuited is therefore varied in accordance with the variations in the strength of the load magnet L.

While I consider the above method of varying the resistance J an important feature of the invention, I wish not to be limited to the precise construction of the load magnet L as. just described, as 13 am well aware that there are many other ways in which the desired results could be accomv plished. The resent construction as shown and described 1s merely illustrative of a simpic way in which the desired operation be obtained. The multiple magnets A and L could be replaced by a series of separate magnetssuitably connected and arranged to operate a series of contacts, and by varyingthewindings of these magnets or their magnetlc circuits similar results could be ob-v tained. As the-car continues to move up-- wardly at reduced speed, the. cam 0 next engages the automatic stop. switch 4 whose nor.- 180 ma'lly closed contacts include the winding 18 of the reversing switch R. These contacts are now opened, thereby breaking the circuit to the reversing switch magnet 18 which becomes de'energized and allows the contacts 10, 12 and 11, 13, respectively, to separate, thereby cutting cit the current supply to the motor and brake magnet B. Since the arallel circuit to. the brakema et incl ing the resistanceB ha's'already een open-cir- I mum cuited .by the automatic stop switch 2, the brake magnet will become denergized substantially instantaneously and the brake will therefore be at once applied with full power to stop the motor.

'From the foregoing it is readily seen that the brake is applied rapidly when the car is stopped automatically at either of the limits of its travel, while the application of the brake at all other positions of the car is more gradual with a corresponding gentle stop of the car.

Should the car for any reason continue to move upwardly after the automatic stop switch l has been opened, the switch 5 will he en 'aged by the cam and have its contacts opened, thereby interrupting the circuit to the potential switch I, causing the latter "to drop its core and connected contacts,

thereby disconnecting the entire system from the. source of electrical supply and at the same time connecting the extra field G through the contacts 39 directly across the motor armature, the dynamic braking action being at its maximum. The stop switch 5 is only opened in case of emergency, as when the other switches l, 2, 3 and 4: refuse to perform their proper functions, and, under ordinary conditions, it is never brought into operation, the operation of the switch 4 being all that is necessary to stop the car automatically at the proper position. The operation of the emergency switch T or the slack cable switch I at any'point of the car travel opens the circuit of the potential switch magnet 33 and stops the car with maximum dynamic braking power, and in some cases I contemplate including the emergency switch T and slack cable switch I in the circuit through the automatic stop switches 2 and 2" so as to have the friction brake applied instantaneously with maxipower, as well as the dynamic brake action.

The operation of the entire system when the car is descending is similar to its opera tion when the car is ascending. In the former case the manually operated switch S is moved to the left, thereby energizing the reversing switch It which operates to start the motor in an opposite direction corre sponding to a descending car. As the car approaches its lower limit of travel the counterweight, or rather the cam l/V carried thereon, operates the automatic stop switches 1, 2, 3, 4 and 5 in succession to slow down and finally stop the car at the desired lower limit of its travel in a manner similar to that before described in connection with an upwardly moving car.

From the foregoing description it is readily seen that the desired distinction or refinement between the .manually efiected stop and the automatic stop at limits is ac accompanying the same shows a complished in a simple andefi'ective manner without the use of a complicated system of electrical circuits or mechanical devices which are liable to disarrangement and uncertain operation at-critical moments.

While the principles involved in my invention are clearly set forth in this applicatic-11 for Letters Patent, and the illustration preferred arrangement of electrical circuits and apparatus embodying my invention, the same admits of wide variation in the constructionand arrangement of parts and of electrical circuits without departing from the spirit and scope of my invention as herein set forth, and I desire not to be limited to the precise arrangement of parts as here shown.

i l hat I claim as new and desire to secure by Letters Patent of the United States 1s 1; In a controlling system, the combination with an electric motor, of .retarding mechanism therefor, automatic means for effecting the operation of said mechanism, and manually controlled means for effecting the operation of said mechanism with a different degree of power.

2. In a controlling system, the combination with an electric motor, of a retarding device therefor, automatic and manual means for efi'ecting the operation-of said device, and means for-reducing the operative power of said device when controlled manually.

3. In s stem of motor control, the combination of an electric motor, resistance in a circuit in parallel to the motor, an electrorespon sive device for varying said resistance, and a plurality of means for effecting the operation of said device to an extent depending on which of said means is operated.

4. In a system of motor control, the combination with an electric motor, of resistance in a circuit in parallel to the motor, electromagnetic apparatus for varying said resistance, a plurality of circuits for said apparatus, and means for impeding the current in one of said circuits-and thereby controlling the extent of operation of said electromagnetic apparatus.

5. In a system of motor control, the combination with an electric motor,-of resistance in a circuit of the motor, an electro-responsive device for effecting a variation in said resistance, a plurality of circuits for said elec'trdresponsive device each arranged to receive current proportional to the voltage of the motor armature, resistance in one of said lastqiamed circuits, and devices for opening and closing the circuits.

5. In a system of motor controhthe combiaziztion with an electric motor, of a sectional resistance in a circuitof the motor, an elec tro-magnet1c device for short-c1rc'u1t1ng one vor more sections of the resistance, a plurality of circuits forsaid elect-ro-magnetic device each adapted to receive current proportional to the voltage at the terminals of the motor armature, means for reducing the current Strength in one ofsaid last-named circuits below that of the other for a predetermined voltage of the motor armature, and devices for opening and closing the circuits.

7. In a system of motor control, the combination with an electric motor, of a dynamic brake circuit, including resistance means for efiecting a variation in said resistance substantially proportional to the speed of the motor, and a second means for eifecting a difierent variation in said resistance also substantially proportional, to the speed of the motor.

' 8. In a system of motor control, the cornbination with an electric motor, of a dyjnamic brake circuit therefor, resistance in said circuit, automatic means for reducing the resistance to amounts varying inversely with thespeed of the motor, and manual means for eflecting a similar reductic'xn of the resistance but'to a different extent for any given speed of the motor.

'9. In a system of motor control, the co bination with an electric motor, of a dynamic brake circuit therefor, sect onal resistance in said circuit, an electromagnet, switches controlled thereby for successively short-circuiting sections'of said resistance,

a plurality of circuits for the electromagnet, a switch in each of said last-named circuits, automatic means for opening and closing one of said switches, a manual device for effecting the opening and closing of the other switch, and a resistance in the manually controlled circuit.

10. In a system of motor control, the combination with a motor, of an electro-dynamic brake therefor, mechanism for varying the power of said brake as the speed of the motor varies, automatic means for bringing said mechanism into operation, manual means for bringing said mechanism into operation, and a device for renderin sald mechanism less efiective when control ed by the manual means. v I

11. In a system of motor control, the combination with an electric motor, of a dynamic brake circuit including resistance in parallel to the armature of the motor, and automatic means for increasin and de-' creasing said resistance substantially in in- Cople: of this patent niay be obtained for live cents each, by addressing the"0ommiuioner of latentl,

the resistance, and means for opening and closing said switches-in a predetermined order and at predetermined speeds of the motor and thereby maintaining a short circuit across an amount of sald resistance varying directly as the speed of the motor.

13. In a system of motor control, the combination with an electric 'motor, of a sectional resistance in a dynamic circuit of the motor, a plurality of switches controlling short circuits across sections of the resistance, and a device for opening and closing one or more of said switches in unison with fluctuations in the speed of the motor and thereby increasing the resistance in said circuit as the speed is reduced and reducing the resistance when the speed is increased.

14. In a system of motor control, the combination with an electric motor, of an electro-dynamic brake circuit connected across the armature and norm-ally open when the motor is running, sectional resistance in said circuit, means for closing the dynamic cir-. cuit, and mechanism for short-circuiting a number of sections of resistance roportional to the speed of the motor an again introducing said sections of resistance suc-V cessively as the speed of the motor falls below predetermined limits.

15. In electrical controlling mechanism,

the combination with an electric motor, of an electromagnetic brake c011, a reslstance in a circult- 1n parallel therewith, circuits and connections for supplying current to said parts, a series of switches, means for successively. operating sald switches at a predetermined period in the operation of the motor, means controlled by the first switch for effecting a reduction in the speed of the motor, a succeeding switch of the series effecting the opening of the resistance circuit, and means controlled by a third switch of the series for cutting off thesupply of current to the motor and brake c011. In testimony whereof, I have signed my name tothis specification in the presence'of two subscribing witnesses.

1 JOHN D. IHLDER.

Witnesses:

C. BLINN, JOHN R. Evans.

Washington, D. 0. 

